1. Field of the Invention
The present invention relates to a non-volatile semiconductor device and a method for automatically recovering an erase failure, and more particularly, to a semiconductor device capable of automatically and quickly recovering an erase failure in which data in a sector cannot be erased within a given time (long-erase failure) and a method of automatically recovering a long-erase failure.
2. Description of the Related Art
A flash memory is known as one of the non-volatile semiconductor devices. The flash memory has sectors each of which is a group of core cells. The conventional flash memory is equipped with a redundant circuit having a redundant sector (spare sector) that is separate from regular sectors (normal sectors) and is provided on the same chip in order to save the device from a failure in any of the regular sectors. A defective regular sector identified by the test/inspection in the fabrication process is replaced by the spare sector. If a long-erase failure occurs in the flash memory chip involved in practical use after shipping, the chip is a “long-erase failure” chip and is handled as a defective chip. If an erase failure is detected by the chip test/inspection step prior to shipping, it may be replaced by a spare sector or the defective chip is discarded by screening.
However, it is eventually difficult to completely implement redundancy and screening for erase failures, and it is inevitable to have an erase failure in practical use after shipping. Japanese Patent Application Publication No. 8-7597 discloses a non-volatile semiconductor memory device enabling automatic recovery from a failure that occurs in practical use by end users. This device is equipped with a circuit that prevents a memory cell having degraded programming or erasing performance from being selected in practical use in order to ensure the good memory performance.
However, the device disclosed in Japanese Patent Application Publication No. 8-7597 erases the sector specified by automatic redundancy, and admits of improvement in reduction of the time necessary for automatic recovery from sector failure.